Atmospheric neutrino fluxes

1
Atmospheric neutrino fluxes

• Status of the calculations
• based on work with M. Honda

2
Outline

• Overview of calculations
• En lt 10 GeV (contained)
• Geomagnetic effects
• Response functions
• Primary spectrum
• Hadronic interactions
• Comparison of calculations
• 3 D effects
• High energy (nm? m ne)
• Importance of kaons
• Calibration of n - telescopes
• Prompt background
• Summary

Distribution of En for 4 classes of events
3
Overview of the calculation
4
Calculations of atmospheric n

• 1 dimensional
• Bartol flux V. Agrawal et al., Phys. Rev. D53
  (1996) 1314
• HKKM M. Honda et al. Phys. Rev. D52 (1995)
  4985
• TKG et al., Hamburg ICRC (2001) p. 1381
• HKKM, Hamburg ICRC (2001) p. 1162
• Fiorentini, Naumov, Villante, Phys. Lett. B510
  (2001) 173
• Used in analysis of Super-K

• 3 dimensional
• G. Battistoni et al., Astropart. Phys. 12 (2000)
  315 -- first 3D calculation
• Y. Tserkovnyak et al., Hamburg ICRC (2001) p.
  1196
• J. Wentz, Hamburg, p. 1167 (complete but
  preliminary)
• Y. Liu et al., Hamburg, p. 1033 (low result ?)
• V. Plyaskin, Phys. Lett. B516 (2001) 213 (just
  revised)

5
Geomagnetic cutoffs E-W effect as a consistency
check

• Picture shows
• 20 GeV protons in geomagnetic equatorial plane
• arrive from West and from near the vertical
• but not from East
• Comparison to data
• provides consistency test of data analysis

From cover of Cosmic Rays by A.M. Hillas (1972)
6
Cutoffs at Super-K

• n flux, 0.4 lt En lt 3 GeV
• -0.5 lt cos(q) lt 0.5
• measured by Super-K and
  compared to 3 calculations

7
Response functions, sub-GeV n

• Eprimary ( 10 ) x En
• Up/down ratio opposite at Kamioka vs Soudan/SNO

8
Solar modulation

• Neutron monitors
• well correlated with cosmic-ray flux
• provide continuous monitor
• response like sub-GeV neutrinos with no cutoff
• SNO, Soudan lt20 variation
• Kamioka lt5 (10 ) for downward (upward)

9
Primary spectrum

• Largest source of overall uncertainty
• 1995 experiments differ by 50 (see lines)
• Present AMS, BESS within 5 for protons
• discrepancy for He larger, but He only 20 of
  nucleon flux
• overall range (neglect highest and lowest)
• /-15, E lt 100 GeV
• /- 30, E TeV

10
Hadronic interactions

• n-yields depend most on treatment of p
  production
• Compare 3 calculations
• Bartol (Target)
• Honda et al. (1995 Fritiof present Dpmjet3)
• Battistoni et al. (Fluka)
• Uncertainties from interactions /-15

11
Comparison (using same flux)

• New calculations lower than old, e.g.
• Target-2.1/ -1
• Dpmjet3 / HKKM
• 3 new calculations agree at Kamioka but not for
  Soudan/SNO
• Larger uncertainty at high geomagnetic l
• Interactions lt 10 GeV are important

12
Comparison (using same event generator)

• sub GeV flux increases slightly using new flux
  from AMS BESS

13
3-dimensional effects

• Characteristic 3D feature
• excess of n near horizon
• shown in top, left panel
• lower panels show directions of m and e
• cannot see 3D effect directly however
• Horizontal excess is associated with a change in
  path-length distribution

From Battistoni et al., Astropart. Phys. 12
(2000) 315
14
3-dimensional effects

• 3D vs 1D comparison at Kamioka (3Dpink
  1D blue/green)
• Dip near horizon
• due to high local horizontal cutoffs
• Size of effect
• pT(p)/Ep sets scale
• 0.1 GeV / En
• therefore negligible for En gt 1 GeV

from M. Honda et al., Phys. Rev. D64 (2001)
053001
15
Path-length dependence

• Path length shorter near horizon on average in 3D
  case
• cos(q) gt 0 only,
• phase space favors nearby interaction scattering
  to large angle
• 5-10 (En 0.3-1 GeV)
• Effect not yet included in Super-K analysis

En 0.3 GeV
En 1 GeV
Soudan/SNO
Kamioka
16
Is the second spectrum important for atmospheric
n?

• Cosmic-ray albedo beautifully measured by AMS at
  380 km
• Biggest effect near geomagnetic equator (vertical
  cutoff 10 GV)
• Albedo sub-cutoff protons from grazing
  interactions of cosmic rays gt cutoff (S.B.
  Treiman, 1953)
• trapped for several cycles
• Re-entry rate is low (dashed line)

17
Comparison to muons

• m, m- vs atmospheric depth
• newer measurements lower by 10-15 than earlier
• comparison not completely internally consistent
• ascent vs float
• balloons rise rapidly
• fraction detected is small compared to m decayed
  to n

Data from CAPRICE, 3D calculation of Engel et al.
(2001)
18
Absolute comparison
19
High energy ( e.g. nm ? m )

• Importance of kaons
• main source of n gt 100 GeV
• p ? K L important
• Charmed analog may be important for prompt leptons

20
Calibration with atmospheric n

• Atmospheric beam well understood
• Thousands of events in km-scale detector
• Example of nm / ne
• flavor ratio
• angular dependence

Note this is maximal effect horizontal 85
- 90 deg in plots
21
Global view of atmospheric n spectrum
Uncertainty in level of charm a potential problem
for finding diffuse neutrinos
22
Uncertainties absolute normalization

• Primary spectrum
• /- 10 up to 100 GeV (using AMS, BESS only)
• /- 20 below 100 GeV, /- 30 TeV (all data)
• Note lack of measurements in TeV range
• Hadronic interactions
• /- 15 below 100 GeV
• 1D o.k. for comparing calculations and for
  tracking effects of uncertainties in input
• Other sources at per cent level
• (local terrain, seasonal variations, anisotropy
  outside heliosphere)
• New measurements HARP, E907
• Uncertainty in sn

23
Summary (low energy)

• Evidence for n oscillation uses ratios
• Contained events
• (ne / nm )data / (ne / nm )calculated
• upward / downward
• Neutrino-induced upward muons
• stopping / through-going
• vertical / horizontal
• Broad response functions minimize dependence on
  slope of primary spectrum
• Uncertainties tend to cancel in comparison of
  ratios
• Observation of geomagnetic effects confirms
  experiment interpretation

24
Summary (high energy)

• Kaon decays dominate atmospheric nm, ne above
  100 GeV
• Well-understood atmospheric nm, ne useful for
  calibration of neutrino telescopes
• Uncertainty in level of prompt neutrinos (from
  charm decay) will limit search for diffuse
  astrophysical neutrinos